The present invention relates generally to retroviral vectors. In particular, the invention relates to retroviral vectors comprising nucleic acid sequences from Gibbon Ape Leukemia Virus.
Considerable effort is now being directed to introducing engineered genes into mammalian cells for a variety of applications including gene therapy and the production of transgenic animals. Such strategies are dependent upon the development of effective means for safe delivery of genes to appropriate target cells and tissues.
Retroviral vectors are particularly useful for directing desired polynucleotides to the appropriate cells and integration of the polynucleotides in the host cell genome. For example, the majority of the approved gene transfer trials in the United States rely on replication-defective retroviral vectors harboring a therapeutic polynucleotide sequence as part of the retroviral genome (Miller et al. Mol. Cell. Biol. 10:4239 (1990); Kolberg R J. NIH Res. 4:43 (1992); Cornetta et al. Hum. Gene Ther. 2:215 (1991)). As is known in the art, the major advantages of retroviral vectors for gene therapy are the high efficiency of gene transfer into certain types of replicating cells, the precise integration of the transferred genes into cellular DNA, and the lack of further spread of the sequences after gene transfer.
Unfortunately, many human cells are not efficiently infected by prior art retroviral vectors. Reduced susceptibility to retroviral infection is most likely due to inefficiencies in one of three stages of viral replication: 1) binding to retroviral receptors on the cell surface and early viral entry, 2) late entry and transport of the viral genome to the cell nucleus and integration of the viral genome into the target cell DNA, and 3) expression of the viral genome. These three stages are governed, respectively, by the viral envelope proteins, the viral core proteins, and the viral genome. All three of these components must function efficiently in a target cell to achieve optimal therapeutic gene delivery.
Gibbon Ape Leukemia Virus (GaLV) uses a cell surface internalization receptor that is different from those of the available retroviral vectors and thus allows infection of cells and tissues normally resistant to retroviral infection. The human receptor for GaLV has recently been cloned and shows a wide cell type and species distribution. Johann et al., J. Virol. 66:1635-1640 (1992). Indeed, GaLV can infect many mammalian species with the notable exception of mouse cells. The same receptor is used by simian sarcoma associated virus (SSAV), a strain of GaLV. Sommerfelt et al., Virol. 176:58-59 (1990).
The construction of hybrid virions having GaLV envelope proteins has been demonstrated. For instance, Wilson et al., J. Virol. 63:2374-2378 (1989), describe preparation of infectious hybrid virions with GaLV and human T-cell leukemia virus retroviral env glycoproteins and the gag and pol proteins of the Moloney murine leukemia virus (MoMLV). In addition, Miller et al., J. Virol. 65:2220-2224 (1991), describe construction of hybrid packaging cell lines that express GaLV envelope and MoMLV gag-pol proteins.
Existent retroviral vectors capable of infecting human cells all contain core and genome components that derive from MoMLV. For human cells which are resistant to efficient infection by such vectors at any of the three stages noted above, new vectors comprising improved envelope, core or regulatory sequences must be designed. Thus, there is a need to design retroviral vectors components which can be used to introduce genes into human cells not efficiently infected by the currently utilized retroviral vectors. The present invention addresses these and other needs.